There are a number of known systems and method for treatment and delivery of therapeutic radiation. One of these is known as three-dimensional conformal radiation therapy (3D-CRT). 3D-CRT involves three-dimensional imaging, accurate radiation dose calculation, computer optimized treatment planning, and computer controlled treatment delivery. In particular, 3D-CRT uses computers and special imaging techniques such as CT, MR or PET scans to show the size, shape and location of a tumor as well as surrounding organs. The therapeutic radiation beams are then precisely tailored to the size and shape of the tumor with multileaf collimators or custom fabricated field-shaping blocks. The precise application of the therapeutic radiation beams results in nearby normal tissue receiving less radiation and so the normal tissue is able to heal more quickly after a therapeutic radiation session. The more normal tissue is shielded from receiving the therapeutic radiation allows for the amount of the radiation actually delivered to the tumor to be increased and so the chances of successfully treating the tumor increase. An example of 3D-CRT is described in the publication, Takahashi S, “Conformation radiotherapy: rotation techniques as applied to radiography and radiotherapy of cancer,” Acta Radiol 1965, Suppl. 242.
Another system and method for treatment planning and delivery of therapeutic radiation is known as intensity-modulated radiation therapy, or IMRT. IMRT is a specialized form of 3D-CRT that allows radiation to be modulated, thus more exactly shaped to fit the tumor. In particular, IMRT involves breaking up the therapeutic radiation beams into many “beamlets.” The intensities of each beamlet are then adjusted individually. Such adjustment of intensities allows for the radiation received by healthy tissue near a tumor to be further reduced when compared with 3D-CRT. An example of IMRT is described in the publication, A. Brahme et al., “Solution of an integral equation encountered in rotation therapy,” Phys Med Biol Vol. 27, No. 10, 1982, pp. 1221-29.
A third system for treatment and delivery of therapeutic radiation is known as intensity modulated arc therapy (IMAT) and later volumetric-modulated arc therapy, also known as VMAT. VMAT addresses several of the disadvantages of IMRT, namely, increased treatment time by requiring a larger number of beam directions and the use of increased monitor units (MU). VMAT addresses these disadvantages by allowing continuous gantry/collimator rotation, leaf motion, and dose rate adjustment for treatment plan optimization where dose is delivered during a single gantry arc of up to 360 degrees. The VMAT technique is similar to tomotherapy in that a full 360 degree range of beam directions are available for optimization, but is fundamentally different from IMRT in that the entire close volume is delivered in a single source rotation. An example of VMAT is described in: 1) Yu C. X. “Intensity-modulated arc therapy with dynamic multileaf collimation: an alternative to tomotherapy,” Phys Med Biol Vol. 40, 1995, pp. 1435-1449, 2) Yu C. X., et al., “Clinical implementation of intensity-modulated arc therapy,” Int J Radiat Oncol Biol Phys Vol. 53, 2002, pp. 453-463 and 3) Otto K., “Volumetric modulated arc therapy: IMRT in a single gantry arc,” Med Phys Vol. 35, 2008. pp. 310-317.
VMAT involves, in part, using multileaf collimator (MLC) leaf motion and dose rate adjustment to modulate beam output intensity. In addition. VMAT delivers the modulated beam intensity output by rotating the gantry and collimator of a linac through one or more complete or partial arcs with the therapeutic radiation continuously on so that treatment times are reduced. During rotation of the gantry, a number of parameters can be dynamically varied, such as: i) the MLC aperture shape, ii) the fluence-output rate (“dose rate”), iii) the gantry rotation speed and iv) the MLC orientation. Being able to vary the parameters i)-iv) allows VMAT to reduce the need to use as many arcs, delivering fewer monitor units (MU) in a shorter time while providing dosimetry comparable to IMRT. While VMAT can take advantage of the above-mentioned four available variable parameters, it must do so while respecting the physical constraints of the linac and MLC—such as the maximum gantry speed, maximum leaf speed, the MLC orientation constraints and the available subdivisions of fluence-output rate.
Without dynamically controlling all machine parameters, specifically the orientations between machine and patient, during treatment delivery, current VMAT technology is limited for certain treatment sites. In the case of breast cancer treatment, it has been shown that VMAT applied to treat left-sided breast cancers with internal mammary node irradiation resulted in an increase in the volume of lungs, heart and contralateral breast receiving low dose (5Gy) irradiation compared to modified wide tangents. By definition, due to its configuration, VMAT used for breast irradiation contains beams directed towards the heart, lungs, and contralateral breast.
Another disadvantage of VMAT systems is that they do not integrate simultaneous kV imaging. Accordingly, such VMAT systems are not capable of real-time treatment verification